In a diffusion transfer process (or a photographic art of forming an image by fixing an imagewise produced diffusible dye on a dye fixing element), a cationic polymer mordant is often used for fixing a diffusible anionic dye on a dye fixing element. In ink jet and thermal dye-transfer methods as well, it has been proposed to use a cationic polymer mordant for fixation of anionic dyes on a dye fixing element.
Polymer mordants as described above are disclosed, for example, in U.S. Pat. Nos. 3,898,088, 3,958,995 and 4,131,469, German Patent (OLS) No. 2,941,818, JP-A-53-30328 and JP-A-56-17352 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
The most important property among those required of such mordants is to impart excellent preservability to images. Although images obtained in accordance with a diffusion transfer process may deteriorate by various mechanisms, two mechanisms in particular pose serious problems from a practical viewpoint. More specifically, one deterioration mechanism relates to movement of dyes inside the dye fixing element or transferring of dyes onto other substances, and the other relates to discoloration of dyes upon exposure to light.
Accordingly, excellent mordants are those having not only high ability to retain and to fix dyes thereon (high mordanting power) but also function to-inhibit the dyes fixed thereon from suffering photo-discoloration.
In this regard, there has been a fair amount of research seeking mordants having the above properties. For example, mention may be made of those disclosed in British Patents 2,011,912, 2,056,101 and 2,093,041, U.S. Pat. Nos. 4,115,124, 4,273,853 and 4,282,305, JP-A-59-232340, JP-A-60-118834, JP-A-60-128443, JP-A-60-122940, JP-A-60-122921, JP-A-60-235134 and so on.
Each of the above-mentioned mordants was somewhat, but not wholly satisfactory. Accordingly, it is still desired to make mordants more satisfactory in the above respects.